http://www.mailscope.io adds profile data to your existing mailing list. Why? Well, if you don't ask for firstname and lastname on signup, you'll get increased conversion. But if you then want to get increased open and click rates when you actually send email, you should start personalizing (one way is to use firstnames in the body) and segmenting. That's where MailScope comes in. Each new subscriber you get, MailScope will automatically add firstname, lastname (and other profile data).
It's just the start and I've been having great fun expanding the possibilities - alerting you when an 'influencer' signs up so that you can reach out directly; auto-following subscribers on twitter when they signup. I've already got a dozen or so paying customers who use MailScope to enrich their mailing lists and increase their revenues. It's awesome to have learnt so much here on HN and finally be able to start offering something of real value back to business owners.